Firing jig for electronic element

ABSTRACT

This invention provides a firing jig for an electronic element comprising a spray coating layer made of a material less reactive to a material to be fired on a substrate made of a ceramic, wherein two or more spray coating layers are formed on the surface of the substrate, and at least a spray coating layer adjacent to the substrate and a spray coating layer adjacent to the material to be fired are made of different materials. When it is a firing jig for an electronic element comprising a ceramic substrate, a surface adjacent to the substrate is a spray coating layer and the surface of the spray coating layer is a flame coating layer. The firing jig for an electronic element has a longer life and can be produced with a lower cost.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

[0001] This invention relates to a firing jig for an electronic element,which has a long life and allows production with a low cost.

[0002] The surface of a firing jig for an electronic element used infiring functional ceramics has been coated with a dense and lessreactive coating material for preventing deterioration in properties ofa material to be fired due to reaction of a component in the firing jigwith the material or absorption of a component in the material in thefiring jig.

[0003] A frequently used substrate for a firing jig is based onAl₂O₃-SiO₂. The material is inexpensive and also highly resistant tothermal shock to allows a firing jig to have a longer life, so that ithas been widely used as a substrate of a firing jig for an electronicelement.

[0004] However, although the outer surface of the jig is coated with adense coating film, repeated firing may cause penetration of SiO₂component in the substrate through the film structure and may remain inthe surface of the jig. Thus, the SiO₂ component may contaminate amaterial to be fired and then may adversely affect the properties of anelectronic element.

[0005] In an alumina-based firing jig, as an Al₂O₃ content increases, acoefficient of thermal expansion increases, so that the jig becomes lessresistant to thermal shock, leading to a shorter life.

[0006] Japanese Patent Laid-Open No. 10-158081 has disclosed that azirconia flame coating film as a coating film may be formed to athickness of 300 μm on the surface of an Al₂O₃-SiO₂-based substrate withan Al₂O₃ content of 65% or higher to improve durability; specifically,detachment of the flame coating layer in the jig may be reduced evenafter repeated cycles of heating and cooling as a firing jig. Such aconfiguration may prevent detachment of the flame coating layer, butproperties of the electronic element placed and fired on the firing jigmay be unstable, resulting in little or no increase in a jig life.

[0007] In view of the problems in the prior art described above, anobjective of this invention is to provide a reliable firing jig for anelectronic element by forming two or more spray coating layers on thesurface of the substrate in the firing jig and defining some factorssuch as the contents of required materials for the substrate andindividual spray coating layers for improving durability of the firingjig and stabilizing performance of the electronic element placed andfired on the firing jig.

SUMMARY OF THE INVENTION

[0008] This invention provides a firing jig for an electronic elementcomprising a substrate made of a ceramic and a spray coating layer madeof a material less reactive to a material to be fired on the substrate,wherein two or more spray coating layers are formed on the surface ofthe substrate, and at least a spray coating layer adjacent to thesubstrate and a spray coating layer adjacent to the material to be firedare made of different materials.

[0009] In a firing jig for an electronic element according to thisinvention, it is preferable that the substrate is mainly based onAl₂O₃-SiO₂, Al₂O₃-SiO₂-MgO or SiC; the spray coating layer adjacent tothe substrate is mainly based on Al₂O₃-SiO₂, Al₂O₃-MgO, Al₂O₃-ZrO₂orAl₂O₃; and the spray coating layer adjacent to the material to befired is mainly based on ZrO₂, Al₂O₃ or Al₂O₃-MgO. An Al₂O₃ content ispreferably 70 to 95 wt % for the substrate, 98 wt % or more for thespray coating layer adjacent to the substrate and 72 to 96 wt % for thetotal in the substrate and the spray coating layer adjacent to thesubstrate.

[0010] An SiO₂ content is preferably 0.5 wt % or less for the spraycoating layer adjacent to the substrate and 0.05 to 0.5 wt % for thespray coating layer adjacent to the material to be fired.

[0011] In a firing jig for an electronic element according to thisinvention, a porosity in each of the spray coating layers is preferably16% or less. The spray coating layers preferably have a crackpenetrating each of these layers with a width of 1 to 5 μm. The totalthickness of the spray coating layers is preferably 50 to 1000 μm. Aparticle size in each of the spray coating layers is preferably 300 μmor less.

[0012] This invention also provides a firing jig for an electronicelement comprising a substrate made of a ceramic and a spray coatinglayer, wherein a surface adjacent to the substrate is the spray coatinglayer and the surface of the spray coating layer is a flame coatinglayer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0013] A firing jig for an electronic element according to thisinvention is based on an alumina-silica material, in which performanceof the electronic element to be placed and fired on the firing jig maybe stabilized by forming two or more spray coating layers on the surfaceof a substrate and defining the contents of the components required forthe substrate and the individual spray coating layers to minimize theamount of SiO₂ entering into the coating layer. This invention will bedescribed with reference to, but of course not limited to, embodimentsbelow.

[0014] The term, “a firing jig for an electronic element” as used hereinmeans a member used for firing of an electronic element made of aceramic such as a ceramic capacitor, a thermistor and ferrite, which maycomprise, for example, a setter, a case, and a plate for placing amaterial to be fired.

[0015] A firing jig of this invention comprises two or more spraycoating layers on the surface of a substrate, where these layers aremade of different materials. Thus, the surfaces adjacent to the surfaceof the substrate and to the material to be fired are spray coatinglayers with a smaller porosity than that in a flame coating layer toprevent a component adversely affecting a work property or deterioratingthe substrate from transferring. Furthermore, if forming a flame coatinglayer, it may be formed by coating with melted ceramic particles, andthus the layer is a solid hard layer so that expansion or shrinkagecannot be absorbed in the layer, causing detachment. On the other hand,in a spray coating layer, particles are mutually sintered to form a softlayer, allowing intralayer relaxation. When a spray coating layer isformed on the surface of the substrate, the layer can prevent a reactivecomponent in the substrate from being in contact with the material ofthe electronic element, allowing a silica-alumina material includingsilica adversely affecting the properties of the electronic element tobe used as a substrate.

[0016] The term “spray coating” as used herein refers to a process ofpreparing a ceramic powder slurry for spraying or applying the slurry onthe surface of the substrate before firing. The term “work property”refers to dispersion of a dielectric constant generated in an electronicelement when firing the electronic element using the firing jig. A goodwork property in a firing jig means that dispersion property of adielectric constant is good in an electronic element fired using thefiring jig.

[0017] The spray coating layers are preferably mainly based onAl₂O₃-SiO₂, Al₂O₃-SiO₂-MgO or SiC. It is preferable that the spraycoating layer adjacent to the substrate is mainly based on Al₂O₃-SiO₂,Al₂O₃-MgO, Al₂O₃-ZrO₂ or Al₂O₃ while the spray coating layer adjacent tothe material to be fired is mainly based on ZrO₂, Al₂O₃ orAl₂O₃-MgO.Such a configuration may provide a firing jig comprising a substratewith good spall resistance and vent resistance, an intermediate layerpreventing a component adversely affecting a material to be fired fromtransferring and the outer layer less reactive to the material to befired.

[0018] In this invention, an Al₂O₃ content is preferably 70 to 95 wt %for the substrate. If the Al₂O₃ content of the substrate is less than70% , a thermal conductivity of the substrate is so reduced that atemperature in the firing jig may significantly vary, leading to anuneven work property on the jig. If the Al₂O₃ content of the substrateis more than 95% , a thermal expansion coefficient of the substrate isso increased that a stress due to temperature variation may besignificantly increased, leading to crack formation. An Al₂O₃ content ispreferably 98 wt % or more for the spray coating layer adjacent to thesubstrate, and the total Al₂O₃ content of the substrate and the spraycoating layer adjacent to the substrate is preferably 72 to 96 wt %.Furthermore, as described later with reference to Examples, an aluminacontent of less than 70 wt % in the substrate may improve heatresistance, but relatively increased silica component may adverselyaffect the properties of an electronic element as a material to befired. The other alumina contents may be limited within the above rangeto stabilize the properties of the electronic element.

[0019] In the present invention, an SiO₂ content is preferably 0.5 wt %or less for the spray coating layer adjacent to the substrate, and 0.05to 0.5 wt % for the spray coating layer adjacent to the material to befired. Thus, dispersion of a component adversely affecting a material tobe fired by passing through the layer adjacent to the substrate as anintermediate layer can be prevented. Furthermore, the SiO₂ content inthe layer adjacent to the material to be fired as the outer layer may belimited within the above range so that absorption of SiO₂ contained inthe material to be fired as a firing aid into the firing jig may beprevented.

[0020] In particular, the spray coating layer adjacent to the materialto be fired must be made of a material less reactive to the material forthe electronic element, but may depend on the type of the electronicelement. For example, since the ceramic condenser is made of bariumtitanate, zirconia less reactive to the material is preferably selected.In this invention, the main component for the coating layer ispreferably one or more selected from the group consisting ofnon-stabilized ZrO₂, Y₂O₃ stabilized ZrO₂, Y₂O₃ partially stabilizedZrO₂, CaO stabilized ZrO₂ and CaO partially stabilized ZrO₂.

[0021] In this invention, a porosity in each of the spray coating layersis preferably 16% or less. Thus, penetration of a component which maydeteriorate a substrate by reacting with the substrate after beingdispersed from the work may be blocked by the spray coating layers, anddispersion of SiO₂ from the substrate to the outer surface may beprevented in firing of a ceramic capacitor, resulting in improvedstability in an electronic element.

[0022] The spray coating layers preferably have a crack penetrating eachof these layers with a width of 1 to 5 μm. In firing of a ceramiccapacitor or ferrite, whose outer surface is often made of zirconia, asthe number of passing through a kiln increases, residual expansioncharacteristic in zirconia may be generated. Since it may cause curvingor detachment in a firing jig, it is effective that a crack as definedabove exists as a room for absorbing such residual expansion.

[0023] The total thickness of the spray coating layers is preferably 50to 1000 μm. Furthermore, as described later in Examples, if thethickness is less than 50 μm, properties of an electronic element firedon the firing jig may vary, while if it is more than 1000 μm, detachmentbetween layers in the firing jig may be often caused when firing anelectronic element using the firing jig. The layer adjacent to thesubstrate must firmly adhere to the substrate. It is preferable that thesurface of a lower layer is coarser for firm adhesion of the lower layerto the layer adjacent to the material to be fired, and coarse particlesmay be appropriately added to the layer adjacent to the substrate as anintermediate layer to make the surface rough, which is suitable tostably hold a layer deposited on the surface layer. However, if anexcessive amount of coarse particles or excessively large particles areused, an adhesive strength in the intermediate layer may be reduced,causing detachment. Furthermore, when the layer adjacent to the materialto be fired as the outer layer is spray-coated, the use of excessivelylarge particles is not preferable because it may reduce an adhesivestrength with the lower layer and detachment may be caused as describedabove. A particle size in each of the spray coating layers is preferably300 μM or less.

[0024] In this invention, an intermediate layer is baked during spraycoating and thus blasting of a substrate or preheating before formingthe intermediate layer may be not necessarily required for preventingdetachment of the intermediate layer from the substrate.

[0025] In a firing jig for an electronic element comprising a ceramicsubstrate of this invention, the surface adjacent to the substrate maybe a spray coating layer, whose surface may be a flame coating layer. Inthis jig, the surface layer is a flame coating layer while the surfaceadjacent to the substrate is a spray coating layer. Thus, thermalexpansion or shrinkage of the substrate and the flame coating layer maybe absorbed. It may prevent deformation of the basedue to detachment ofthe flame coating layer or residual expansion in the flame coatinglayer.

[0026] The term “flame coating” as used herein refers to a process forforming a flame coating film by melting metal or ceramic fine powder(hereinafter, referred to as “flame coating material”) by heating andthen spraying it onto an object. There may be variations such as gasflame coating using flame and arc flame coating using arc depending on aheating method. In this invention, it is preferable to form an outerflame coating film by plasma flame coating using a plasma jet.

[0027] In this invention, particularly preferable plasma flame coatingis water-stabilized plasma flame coating. The minimum film thickness ofa flame coating film by gas plasma flame coating is about 20 to 50 μmbecause a thick coating film with the minimum film thickness of about100 μm may be formed by water-stabilized plasma flame coating. Sincewater-stabilized plasma flame coating may form a coating film with arelatively porous and coarse surface, it is also preferable in terms ofimprovement of adhesiveness to the surface of the spray coating layeradjacent to the substrate.

[0028] This invention will be more specifically described with referenceto, but not limited to, Examples.

[0029] (Examples 1 to 9 and Comparative Examples 1 to 5)

[0030] A material consisting of Al₂O₃ to a content shown in Table 1 andSiO₂ and MgO as the remaining components was pressed and fired to form aplate with the dimensions of a 200 mm (length)×200 mm (width)×5 mm(thickness) as a substrate. A firing temperature was appropriatelyvaried in the light of an alumina content. On the surface of thesubstrate were formed a spray coating layer adjacent to the substrate(made of Al₂O₃, thickness: 100 μm) and a spray coating layer adjacent tothe material to be fired (made of ZrO₂, thickness: 100 μm) by spraycoating to produce a firing jig. Alternatively, on the surface of thesubstrate were formed a spray coating layer adjacent to the substrate byspray coating and a flame coating layer adjacent to the material to befired by plasma flame coating to produce a firing jig.

[0031] Table 1 shows component(s) for a substrate and an alumina contentin each example; processes used for forming a layer adjacent to asubstrate and a layer adjacent to a material to be fired; and theresults obtained.

[0032] (Evaluation procedures)

[0033] (1) Spalling test

[0034] On the above jig was evenly applied alumina abrasive grains withan average particle size of 2 mm and it was repeatedly passed through aroller hearth kiln under the conditions of the maximum temperature of1300° C. and 9 hrs from an inlet to an outlet (warming: 3 hrs,retention: 3 hrs, cooling: 3 hrs). Then, presence of cracks generated bythermal spall and a length of a crack were determined.

[0035] (2) Reaction curving test

[0036] On the jig was applied a solution of barium titanate as adielectric, and it was repeatedly fired in a small electric furnace at1400° C. for 2 hours to determine the firing number until anintermediate layer (or a coating layer) was detached from the substrateor a crack was generated due to curving of the jig.

[0037] (3) Detachment test

[0038] This test was conducted as described in the above reactioncurving test.

[0039] (4) Work property test

[0040] On the above jig was placed a barium titanate sheet formed by adoctor-blade method. After firing it in a small electric furnace at1350° C. for 2 hours, a dielectric constant was determined. TABLE 1Method for Substrate Method for forming a layer Al₂O₃ forming a layeradjacent to a Evaluation content adjacent to a material to be ReactionDetach- Work Material (%) substrate fired Spalling curving ment propertyComparative Al₂O₃—SiO₂ 85 Flame coating Flame coating ; x ; ; Example 1Example 1 Al₂O₃—SiO₂ 85 Spray Flame coating ; ; T T Example 2 Al₂O₃—SiO₂85 Spray Spray ; T T T Example 3 Al₂O₃—SiO₂—MgO 85 Spray Spray T ; ; TExample 4 SiC — Spray Spray T T ; ; Comparative Al₂O₃—SiO₂ 65 SpraySpray T ; ; x Example 2 Comparative Al₂O₃—SiO₂ 69 Spray Spray T ; ; ΔExample 3 Example 5 Al₂O₃—SiO₂ 70 Spray Spray T T T ; Example 6Al₂O₃—SiO₂—MgO 80 Spray Spray T T T T Example 7 Al₂O₃—SiO₂ 80 SpraySpray T T T T Example 8 Al₂O₃—SiO₂ 90 Spray Spray ; T T T Example 9Al₂O₃—SiO₂ 95 Spray Spray ; T T ; Comparative Al₂O₃—SiO₂ 96 Spray SprayΔ ; T ; Example 4 Comparative Al₂O₃—SiO₂ 100 Spray Spray x ; T ; Example5

[0041] (Evaluation)

[0042] As shown in Table 1, reaction curving was observed in ComparativeExample 1 in which the layer adjacent to the substrate is a flamecoating layer. Comparative Examples 2 and 3 in which an Al₂O₃ content ofthe substrate is less than 70% exhibited a poor work property, whileComparative Examples 4 and 5 in which the content is more than 95%exhibited poor spalling property.

[0043] A jig where a spray coating layer and further spray coating andflame coating layers were formed on the surface of the ceramic substrateexhibited satisfactory function as a firing jig for an electronicelement even when the substrate was made of Al₂O₃-SiO₂-MgO as long asits Al₂O₃ content was within the range of 70 to 95 wt %. Similar resultswere obtained for a substrate based on SiC without Al₂O₃.

[0044] Evaluation is herein indicated in the tables according to thefollowing rating: T: very good, ;: good, Δ: slightly insufficient, x:insufficient.

[0045] (Examples 10 to 12 and Comparative Examples 6 and 7)

[0046] Firing jigs were produced as described in Examples 1 to 9, exceptthat a Al₂O₃-SiO₂ material with an Al₂O₃ content of 85% was used for asubstrate; the layers adjacent to the substrate (thickness: 100 μm) andto the material to be fired (thickness: 100μm) were formed using spraycoating layers; and the layer adjacent to the substrate was made ofAl₂O₃. Table 2 shows an Al₂O₃ content in the layer adjacent to thesubstrate and the evaluation results. TABLE 2 Layer adjacent to asubstrate Evaluation Al₂O₃ content Reaction Work (%) curving Detachmentproperty Example 10 99.9 ; T T Example 11 99.0 ; T T Example 12 98 ; T ;Comparative 97.9 ; ; Δ Example 6 Comparative 97 ; ; x Example 7

[0047] (Evaluation)

[0048] As shown in Table 2, a work property was insufficient inComparative Examples 6 and 7, in which an Al₂O₃ content was less than98% in the spray coating layer adjacent to the substrate. It might bebecause a work property was adversely affected by a relatively large (2%or more) amount of SiO₂ coexisting with Al₂O₃ in the coating layeradjacent to the substrate.

[0049] (Examples 13 to 21 and Comparative Examples 8 and 9)

[0050] Firing jigs were produced as described in Examples 1 to 9, exceptthat a material shown in Table 3 was used for a substrate; the layersadjacent to the substrate (thickness: 100 μm) and to the material to befired (thickness: 100 μm) were formed using spray coating layers; andthe layer adjacent to the substrate was made of a material shown inTable 3.

[0051] Table 3 shows a material and an Al₂O₃ content in the substrate, amaterial for the layer adjacent to the substrate, a total Al₂O₃ contentin the substrate and the layer adjacent to the substrate, and theevaluation results. TABLE 3 Substrate Layer Total Al₂O₃ adjacent toAl₂O₃ Evaluation content the substrate content Reaction Detach- WorkMaterial (%) Material (%) Spalling curving ment Property ComparativeAl₂O₃—SiO₂ 70 Al₂O₃ 71 T ; Δ Δ Example 8 Example 13 Al₂O₃—SiO₂ 70 Al₂O₃72 T T ; ; Example 14 Al₂O₃—SiO₂— 80 Al₂O₃ 81 T T T T MgO Example 15Al₂O₃—SiO₂ 80 Al₂O₃ 81 T T T T Example 16 Al₂O₃—SiO₂ 80 Al₂O₃—MgO 81 T TT ; Example 17 Al₂O₃—SiO₂ 80 Al₂O₃—ZrO₂ 81 T T T ; Example 18 Al₂O₃—SiO₂80 Al₂O₃ 82 T T T T Example 19 Al₂O₃—SiO₂ 85 Al₂O₃ 86 ; T T T Example 20Al₂O₃—SiO₂ 90 Al₂O₃ 91 ; ; T ; Example 21 Al₂O₃—SiO₂ 95 Al₂O₃ 96 ; ; ; ;Comparative Al₂O₃—SiO₂ 95 Al₂O₃ 97 Δ ; ; ; Example 9

[0052] (Evaluation)

[0053] As shown in Table 3, detachment and work property results wereinsufficient in Comparative Example 8 in which the total Al₂O₃ contentin the substrate and the spray coating layer adjacent to the substratewas less than 72%. It might be because an inadequate Al₂O₃ content inthe substrate reduced a thermal conductivity of the substrate to make awork property in the jig uneven and to increase a thermal expansiondifference between the substrate and the spray coating layer so thattendency to detachment was increased. In addition, spalling wasinsufficient in Comparative Example 9 in which the total Al₂O₃ contentwas more than 96%. It might be because increase in the total Al₂O₃content in the substrate caused increase in thermal expansion, leadingto the insufficient spalling result.

[0054] The results show that even Al₂O₃-MgO or Al₂O₃-ZrO₂ may be used asa material for the spray coating layer adjacent to the substrate toprovide a good firing jig for an electronic element as long as the totalAl₂O₃ content in the substrate and the spray coating layer adjacent tothe substrate is within the defined range.

[0055] (Examples 22 to 28 and Comparative Example 10)

[0056] Firing jigs were produced as described in Examples 1 to 9, exceptthat a Al₂O₃-SiO₂ material with an Al₂O₃ content of 80% was used for asubstrate; the layers adjacent to the substrate (thickness: 100 μm) andto the material to be fired (thickness: 100 μm) were formed using spraycoating layers; and the layer adjacent to the substrate was made of amaterial shown in Table 4.

[0057] Table 4 shows a material and an SiO₂ content of the layeradjacent to the substrate, and the evaluation results. TABLE 4 Layeradjacent to the substrate Evaluation Material SiO₂ content (%) SpallingDetachment Work property Comparative Al₂O₃ 0.60 Δ ; Δ Example 10 Example22 Al₂O₃ 0.50 ; ; ; Example 23 Al₂O₃ 0.30 ; T ; Example 24 Al₂O₃—MgO0.30 ; ; ; Example 25 Al₂O₃—ZrO₂ 0.30 ; ; ; Example 26 Al₂O₃ 0.10 T T TExample 27 Al₂O₃ 0.05 T T T Example 28 Al₂O₃ 0.01 T T T

[0058] (Evaluation)

[0059] As shown in Table 4, reaction curving and work property resultswere insufficient in Comparative Example 10 in which the SiO₂ content inthe spray coating layer adjacent to the substrate was more than 0.5%.The results also show that even Al₂O₃-MgO or Al₂O₃-ZrO₂ may be used as amaterial for the spray coating layer adjacent to the substrate toprovide a good firing jig for an electronic element as long as a SiO₂content in the spray coating layer adjacent to the substrate is withinthe defined range.

[0060] (Examples 29 to 34 and Comparative Example 11)

[0061] An Al₂O₃-SiO₂ material with an Al₂O₃ content of 85% was pressedand fired at 1500° C. to give a plate with the dimensions of 140 mm(length)×140 mm (width)×5 mm (thickness), which was used as a substrate.On the plate member was sprayed slurried alumina or mullite particles,and the plate was fired at 1450° C. to form a spray coating layeradjacent to the substrate. On the layer was formed a layer adjacent to amaterial to be fired using yttria-stabilized zirconia, alumina-magnesiaspinel or alumina by spray coating or plasma flame coating. The productwas evaluated for its curving and detachment after repeating adurability test three times. A test product as a comparative example wasprepared by forming a layer adjacent to the substrate using alumina as amaterial by plasma flame coating, forming thereon a layer adjacent to amaterial to be fired using yttria-stabilized zirconia as a materialsimilarly by plasma flame coating and then firing the product. Table 5shows the results. TABLE 5 Layer adjacent to the Layers adjacent to amaterial substrate to be fired Evaluation Material Process MaterialProcess Curving Detachment Example 29 Alumina Spray* Yttria-stabilizedSpray None None zirconia Example 30 Alumina Spray Yttria-stabilizedFlame coating None None zirconia Example 31 Alumina SprayAlumina-magnesia Spray None None spinel Example 32 Alumina SprayAlumina-magnesia Flame coating None None spinel Example 33 Mullite SprayAlumina Spray None None Example 34 Mullite Spray Alumina Flame coatingNone None Comparative Alumina Flame coating** Yttria-stabilized Flamecoating ≧2 mm None Example 11 zirconia

[0062] (Evaluation)

[0063] As shown in Table 5, reaction curving was insufficient inComparative Example 11 (≧2 mm) in which the layer adjacent to thesubstrate was formed by flame coating. When the layer adjacent to thesubstrate was formed by spray coating, the layer adjacent to a materialto be fired as a surface layer could be either a spray coating or flamecoating layer to exhibit good reaction curving and detachment resultseven when the latter layer was made of any material of yttria-stabilizedzirconia, alumina-magnesia spinel and alumina.

[0064] (Examples 35 to 42 and Comparative Examples 12 to 15)

[0065] An Al₂O₃-SiO₂ material with an Al₂O₃ content of 85% was pressedand fired at 1500° C. to give a plate with the dimensions of 140 mm(length)×140 mm (width)×5 mm (thickness), which was used as a substrate.On the plate member was sprayed slurried alumina particles with an Al₂O₃content of 99.9%, and the plate was fired at 1450° C. to form a spraycoating layer adjacent to the substrate. On the layer was formed a layeradjacent to a material to be fired using yttria-stabilized zirconia withan SiO₂content of 0.03 to 0.7% by spray coating. The plate was fired toproduce a firing jig.

[0066] On each sample was placed a barium titanate sheet and then it wasfired, at the end of which dispersion of a dielectric constant wasdetermined for evaluating dispersion in a work property. The product wasevaluated for its curving and detachment after repeating a durabilitytest three times. Table 6 shows the results. TABLE 6 Layer adjacent to amaterial to be fired Evaluation SiO₂ content Dispersion of a Durationtest (%) work property Curving Detachment Comparative 0.03 Small NoneObserved Example 12 Comparative 0.04 Small None Observed Example 13Example 35 0.05 Small None None Example 36 0.06 Small None None Example37 0.07 Small None None Example 38 0.1 Small None None Example 39 0.2Small None None Example 40 0.3 Small None None Example 41 0.4 Small NoneNone Example 42 0.5 Small None None Comparative 0.6 Medium None NoneExample 14 Comparative 0.7 Large None None Example 15

[0067] (Evaluation)

[0068] As shown in Table 6, detachment was observed in ComparativeExamples 12 and 13 in which an SiO₂ content was less than 0.05% in thespray coating layer adjacent to a material to be fired, while dispersionin a capacitance was insufficient in Comparative Examples 14 and 15, inwhich an SiO₂ content was more than 0.5%. Good results for acapacitance, reaction curving and detachment were obtained in the othersamples where an SiO₂ content was within the defined range.

[0069] (Examples 43 to 48 and Comparative Examples 16 to 19)

[0070] An Al₂O₃-SiO₂ material with an Al₂O₃ content of 85% was pressedand fired at 1550° C. to give a plate with the dimensions of 140 mm(length)×140 mm (width)×5 mm (thickness), which was used as a substrate.On the plate member was sprayed slurried alumina particles with anaverage particle size of 10 μm or 90 μm, and the plate was fired at1300° C. or 1550° C., respectively to form a spray coating layeradjacent to the substrate having a different porosity. On the layer wasformed a layer adjacent to a material to be fired usingyttria-stabilized zirconia by spray coating. The plate was fired toproduce a firing jig. For a comparative example, a layer adjacent to thesubstrate was formed as a flame coating layer with a different porosityby plasma flame coating varying a size of alumina particles. The resultsare shown in Table 7. TABLE 7 Layer adjacent to the substrate PorosityEvaluation Process (%) Curving Detachment Example 43  Spray* 0.2 NoneNone Example 44 Spray 1.7 None None Example 45 Spray 3.5 None NoneExample 46 Spray 8 None None Example 47 Spray 11 None None Example 48Spray 16 None None Comparative Spray 18 Observed None Example 16Comparative  Flame coating** 21 Observed None Example 17 ComparativeFlame coating 26 Observed Observed Example 18 Comparative Flame coating30 Observed Observed Example 19

[0071] (Evaluation)

[0072] When forming a layer adjacent to the substrate by spray coating,good curving and detachment results were obtained in a durability testbecause the layer had a smaller porosity, i.e., less voids, than a layerformed by plasma flame coating.

[0073] (Examples 49 to 51 and Comparative Examples 20 to 22)

[0074] An Al₂O₃-SiO₂ material with an Al₂O₃ content of 90% was pressedand fired at 1550° C. to give a plate with the dimensions of 140 mm(length)×140 mm (width)×5 mm (thickness), which was used as a substrate.On the plate member was sprayed slurried alumina particles with an Al₂O₃content of 99.9% , and the plate was fired at 1500° C. to forma spraycoating layer adjacent to the substrate. On the layer was formed a layeradjacent to a material to be fired using yttria-stabilized zirconia withan SiO₂ content of 0.05 to 0.70% by spray coating. The plate was firedat 1500° C. to produce a firing jig. The results are shown in Table 8.TABLE 8 Curving after a durability test Detachment after a durabilitytest Void (the number of repetition) (the number of repetition) (μm) 3 69 3 6 9 Example 49 1 None None Observed None None None Example 50 3 NoneNone None None None None Example 51 4 None None None None None NoneComparative 7 None None None None None Observed Example 20 Comparative10 None None None None Observed Observed Example 21 Comparative 20 NoneNone None None Observed Observed Example 22

[0075] (Evaluation)

[0076] In a product in which a crack with a width of 1 to 5 μm could beformed penetrating layers adjacent to the substrate and adjacent to amaterial to be fired after producing as described above, zirconiaresidual expansion was absorbed in the layer adjacent to a material tobe fired, resulting in delay of detachment generation.

[0077] (Examples 52 to 61 and Comparative Examples 23 to 27)

[0078] An Al₂O₃-SiO₂ material with an Al₂O₃ content of 85% was pressedand fired at 1500° C. to give a plate with the dimensions of 140 mm(length)×140 mm (width)×5 mm (thickness), which was used as a substrate.On the plate member was sprayed slurried alumina particles with an Al₂O₃content of 99.9%, and the plate was fired at 1450° C. to form a spraycoating layer adjacent to the substrate. On the layer was formed a layeradjacent to a material to be fired using yttria-stabilized zirconia withan SiO₂ content of 0.05 to 0.70% by spray coating. The plate was firedat 1450° C. to produce a firing jig.

[0079] In Examples, spray coating was conducted independently varyingthe thicknesses of the layers adjacent to the substrate and to amaterial to be fired for evaluating effects of the thicknesses on theproperties of a fired material and detachment. The results are shown inTable 9. TABLE 9 Thickness of a spray coating layer Layer Layer adjacentadjacent to a Property to the material test sub- to be Total DispersionDurability strate fired thickness in a work test (μm) (μm) (μm) propertyDetachment Comparative 0 30 30 Large None Example 23 Comparative 10 3040 Medium None Example 24 Example 52 20 30 50 Small None Example 53 5050 100 Small None Example 54 100 100 200 Small None Example 55 100 200300 Small None Example 56 200 300 500 Small None Example 57 300 400 700Small None Example 58 300 500 800 Small None Example 59 400 500 900Small None Example 60 500 500 1000 Small None Example 61 300 700 1000Small None Comparative 400 700 1100 Small Observed Example 25Comparative 500 700 1200 Small Observed Example 26 Comparative 600 7001300 Small Observed Example 27

[0080] (Evaluation)

[0081] As shown in Table 9, a dispersion in a work property of a firedmaterial was increased in Comparative Examples 23 and 24, in which thetotal thickness of the spray coating layers was less than 50 μm, while adetachment result was insufficient in Comparative Examples 25, 26 and27, in which the thickness was more than 1000 μm. It was because anexcessively small total thickness of two layers, i.e., the spray coatinglayers adjacent to the substrate and to a material to be fired,adversely affected the fired material so that component dispersion couldnot be prevented. On the other hand, an excessively large totalthickness might reduce adhesiveness of the substrate to the spraycoating layer adjacent to the substrate in relation to the thickness,resulting in detachment.

[0082] When the total thickness of the spray coating layers was withinthe defined range, results for dispersion in a work property anddetachment were sufficient.

[0083] (Examples 62 to 65 and Comparative Examples 28 and 29)

[0084] An Al₂O₃-SiO₂ material with an Al₂O₃ content of 85% was pressedand fired at 1550° C. to give a plate with the dimensions of 140 mm(length)×140 mm (width)×5 mm (thickness), which was used as a substrate.On the plate member was sprayed slurried alumina particles with themaximum particle size of 80 μm to 500 μm containing alumina fine powder,and the plate was fired at 1500° C. to form a spray coating layeradjacent to the substrate. On the layer was formed a layer adjacent to amaterial to be fired using yttria-stabilized zirconia by spray coating.The plate was fired at 1500° C. to produce a firing jig. The results areshown in Table 10. TABLE 10 Layer adjacent to the substrate Maximumparticle size of Al₂O₃ Durability test (μm) Detachment Example 62 80None Example 63 120 None Example 64 250 None Example 65 300 NoneComparative 400 Observed Example 28 Comparative 500 Observed Example 29

[0085] (Evaluation)

[0086] As shown in Table 10, a detachment result was insufficient inComparative Examples 28 and 29, in which a particle size in each spraycoating layer was larger than 300 μm. When the particle size was withinthe defined range, good results were obtained for detachment.

[0087] As described above, in a firing jig for an electronic elementaccording to this invention, two or more spray coating layers are formedon the surface of the substrate in the firing jig and contents ofmaterials required are defined for the substrate and the individualspray coating layers so that durability of the firing jig can beimproved and performance of an electronic element placed and fired onthe firing jig can be stabilized.

What is claimed is:
 1. A firing jig for an electronic element comprisinga substrate made of a ceramic and a spray coating layer made of amaterial less reactive to a material to be fired on the substrate,wherein two or more spray coating layers are formed on the surface ofthe substrate, and at least a spray coating layer adjacent to thesubstrate and a spray coating layer adjacent to the material to be firedare made of different materials.
 2. The firing jig for an electronicelement according to claim 1, wherein the substrate is mainly based onAl₂O₃-SiO₂, Al₂O₃-SiO₂-MgO or SiC; the spray coating layer adjacent tothe substrate is mainly based on Al₂O₃-SiO₂, Al₂O₃-MgO, Al₂O₃-ZrO₂ orAl₂O₃; and the spray coating layer adjacent to the material to be firedis mainly based on ZrO₂, Al₂O₃ or Al₂O₃-MgO.
 3. The firing jig for anelectronic element according to claim 1, wherein an Al₂O₃ content in thesubstrate is 70 to 95 wt %.
 4. The firing jig for an electronic elementaccording to claim 1, wherein an Al₂O₃ content in the spray coatinglayer adjacent to the substrate is 98 wt % or more.
 5. The firing jigfor an electronic element according to claim 1, wherein the total Al₂O₃content in the substrate and the spray coating layer adjacent to thesubstrate is 72 to 96 wt %.
 6. The firing jig for an electronic elementaccording to claim 1, wherein an SiO₂ content in the spray coating layeradjacent to the substrate is 0.5 wt % or less.
 7. The firing jig for anelectronic element according to claim 1, wherein an SiO₂ content in thespray coating layer adjacent to the material to be fired is 0.05 to 0.5wt %.
 8. The firing jig for an electronic element according to claim 1,wherein a porosity in each of the spray coating layers is 16% or less.9. The firing jig for an electronic element according to claim 1,wherein the spray coating layers have a crack penetrating each of theselayers with a width of 1 to 5 μm.
 10. The firing jig for an electronicelement according to claim 1, wherein the total thickness of the spraycoating layers is 50 to 1000 μm.
 11. The firing jig for an electronicelement according to claim 1, wherein a particle size in each of thespray coating layers is 300 μm or less.
 12. A firing jig for anelectronic element comprising a substrate made of a ceramic and a spraycoating layer, wherein a surface adjacent to the substrate is the spraycoating layer and the surface of the spray coating layer is a flamecoating layer.